The following two weeks were full of activity. After a successful weekend spent with Samantha, a lot of progress had been made in planning the wedding, Penny had started a few classes at the community college, and Leonard had officially moved out of his and Sheldon's apartment. A week and half had passed since Leonard had left, and neither he nor Penny had heard a word from him since then. Sheldon had made Leonard return his key, so they couldn't stop by and check on him. While they were concerned, they didn't see much they could do about it.

While Penny was studying for a test in the physics class she was taking in an attempt to understand Leonard's work, she became completely stuck. She thought about waiting for Leonard to get home and asking him for help, but she really wanted to keep it as a surprise for him. She decided to go across to hall to see if Sheldon would help her.

Unlike their earlier attempts, when Penny knocked on the door, she didn't say who it was. After a few moments, Sheldon opened the door. She smiled at him, but it was not returned.

"Hello, home-wrecker," he greeted her.

"Sheldon, don't say that," Penny said.

"Why not? It's the truth." Sheldon pointed to the books she was holding. "What are those?"

"These are textbooks," Penny said, holding them up.

"'General Physics' and 'Introduction to College Algebra,'" Sheldon read. "What would you need these for?"

"I'm taking a math class and a physics class because I want to try to understand Leonard's work," Penny explained.

"Leonard's work is nothing extraordinarily difficult to comprehend, but these high school textbooks aren't going to get you anywhere," Sheldon told her.

"They're not high school! They're college!" Penny held up the math book. "See? Says right there. College Algebra."

"But Leonard's work, while admittedly rather simplistic, is still at the graduate level, not community college. Therefore, your attempts to learn are futile," Sheldon said.

"Sheldon, just because you're mad at me for taking your roommate doesn't mean you can be cruel," Penny told him.

"I'm not being cruel. I'm telling you the truth. You'll never be able to understand Leonard's work."

"Okay, this was a mistake. I'm leaving," Penny said as she turned around and took a few steps away.

"What did you come here for in the first place?" Sheldon wondered.

"Because I'm an idiot, I came here hoping you would tutor me," Penny told him.

"Oh. Well, why didn't you say so?"

"What?"

"As a dedicated scientist, I have a responsibility to teach the ignorant about the mechanics of the physical world. Or, in your case, attempt to teach," Sheldon said, making Penny scowl. "Come inside. I'll do what I can."

"I am seriously going to regret this," Penny said as she entered the apartment. They settled on the couch and Sheldon took her textbooks.

"So what are you having trouble with?" Sheldon asked.

"Kinematics."

"And what's confusing you about that?"

"Everything."

"Oh, we do have a lot of work to do," Sheldon said. "Kinematics is the branch of classical mechanics which describes the motion of points, objects, and groups of objects, without consideration of the causes of motion."

"Why would you want to study motion without considering what causes motion?" Penny wondered.

"You do realize that a key part of learning is attending class, don't you?" Sheldon asked.

"I do attend class, Sheldon, I just…"

"What?"

"I just don't understand what's happening in class," Penny told him.

"Penny, can I ask you a question?"

"I know I'm also going to regret this, but sure."

"Why are you wasting your time and money attempting to study physics and math when you know that you don't have the intelligence level to comprehend it?" Sheldon asked.

"Can I ask you a question?"

"But you didn't answer mine."

"Good observation. Why do you constantly have to put people down?"

"I don't put people down, Penny. I merely tell them the truth that no one else seems to be willing to say," Sheldon said emotionlessly.

"People don't say it for a reason," Penny said. "You can't go around telling people that they're stupid and that their work is meaningless."

"But it's true."

"It's not true!" Penny exclaimed. "Leonard's work is not meaningless. He's discovering important information about the universe, I know that much. And I know that I'm not book smart like you and Leonard, but I am a lot more street smart than you, and you can't deny that."

"Book smart and street smart? What are you, a gangster?" Sheldon asked.

"No. Book smart means you're smart in math and science and that stuff. Street smart means you know how to act like a human being! You try to tell me that I'm not more street smart than you!"

"Penny, you're yelling at me," Sheldon stated.

"Yeah, because I'm frustrated!" Penny said. "I know you're upset with me, but I have enough people telling me that I'm stupid right now. I don't need someone who for some reason I consider to be a friend to tell me that, too!"

"I'm not upset with you."

"Yes, you are! If you weren't upset with me and Leonard, then you would be talking to us and letting us into the apartment when we try to come over," Penny said.

"I'm only frustrated because Leonard violated the roommate agreement. He moved out without submitting a written notice and didn't wait the five weeks."

"No, that's not why you're upset. You're upset because you don't have Leonard around to be your playmate anymore," Penny said. "I'm sorry things are changing, Sheldon, but you have to understand that life without change isn't life."

"I don't understand," Sheldon said.

"Change is what drives life. If you don't have change, then you're not living," Penny said. "If everything stayed the same forever, then there wouldn't be any opportunity to change and adapt and grow."

"But I don't want to change or adapt or grow," Sheldon said.

"I know you don't. But I'm trying to make you understand that you have to do all of those things because that's what makes us human—evolution."

"Well…when you put it that way…Evolution is a necessity for the survival of our species, so perhaps it's not such a bad thing," Sheldon said after a minute of thought.

"It really isn't. I know this evolution is going do be strange, but it's also going to offer a lot of new opportunities, like when humans got opposable thumbs," Penny said, realizing she had found a way to make him understand.

"I'm not sure I see the positive outcomes this evolution could cause," Sheldon said.

"Well, it could give you a chance to meet someone new if you get another roommate," Penny proposed. "It could give you the opportunity to create some new theories in peace now that you won't have someone around to distract you."

"That is true. Imagine the kinds of discoveries I could make without you and Leonard around crying to a deity that neither of you believe in," Sheldon said.

"I was thinking, you know, Leonard watching TV, but okay," Penny commented, shaking her head. "See? There are a lot of great things coming for all three of us from Leonard moving out."

"Penny?"

"Yeah?"

"Is Leonard happy?" Sheldon asked. Penny smiled as she began to melt once she was finally starting to see a human part of him.

"Yes, Sheldon. Leonard is very happy," Penny assured him.

"You know…I am glad you're engaged," Sheldon said.

"Really?" Penny asked, surprised. Sheldon nodded. "Why?"

"Because whenever you two were not in a relationship, all Leonard could talk about was ways that he could get you to like him. Then when you broke up with him, all he could talk about was how he could get you back," Sheldon explained. "The only time he was truly tolerable to live with because he wasn't constantly moping around was when you were in a relationship together."

"That is the sweetest thing ever," Penny said with a big smile.

"But I still don't see why he had to move out," Sheldon said, ending the moment. Penny sighed, knowing he was hopeless.

"Well, thank you for mostly understanding," she said. "Do you think you could try to tutor me again?"

"I don't know if that's a great idea," Sheldon said.

"Why not?"

"It would be a waste of my valuable time now that I have the peace I need to create truly groundbreaking theories," Sheldon explained. "I know you don't want to hear this, Penny, but you're hopeless."

"Alright. Great talking to you, too," Penny said as she grabbed her books and headed across the hall to her apartment. She closed the door and threw her books on the coffee table, mentally exhausted from the exchange she had just had with Sheldon. She flopped onto the couch and cracked open her books again, determined to get some studying done before Leonard got home. However, the subject was so dull to her, she ended up thinking about what had just happened. She knew what Sheldon didn't: while she may have been hopeless in physics, he was equally hopeless in a very different way.